Science Class 11 - Waves Notes

Waves

Welcome to the chapter on Waves for Class 11. In this chapter, you will learn about the nature of waves, their types, properties, and how they are described mathematically. By the end of this chapter, you will understand the basic principles of wave motion and their applications in real life and science.

Introduction

Waves are disturbances that transfer energy from one place to another without the transfer of matter. Waves are everywhere: in water, sound, light, and even in the movement of strings and springs.

Types of Waves

• Mechanical Waves: Require a medium to travel (e.g., sound waves, water waves).
• Electromagnetic Waves: Do not require a medium (e.g., light, radio waves).
• Transverse Waves: The particles of the medium move perpendicular to the direction of wave propagation (e.g., light waves, waves on a string).
• Longitudinal Waves: The particles of the medium move parallel to the direction of wave propagation (e.g., sound waves).

Key Terms

• Crest: The highest point of a wave.
• Trough: The lowest point of a wave.
• Amplitude (A): The maximum displacement from the mean position.
• Wavelength (λ): The distance between two consecutive crests or troughs.
• Frequency (f): The number of waves passing a point per second (measured in Hertz, Hz).
• Time Period (T): The time taken for one complete wave to pass a point (T = 1/f).
• Wave Speed (v): The speed at which the wave travels (v = f × λ).

Wave Equation

The basic equation relating speed, frequency, and wavelength is:

v = f × λ

where v is the speed of the wave, f is the frequency, and λ is the wavelength.

Properties of Waves

• Reflection: Waves bounce back when they hit a barrier.
• Refraction: Waves change direction when they enter a different medium.
• Diffraction: Waves spread out after passing through a small opening.
• Interference: When two waves meet, they can add up (constructive) or cancel out (destructive).

Applications of Waves

• Sound waves help us hear.
• Light waves help us see.
• Radio and TV signals use electromagnetic waves.
• Seismic waves help us study earthquakes.

Practice Questions

1. Define wavelength and frequency.
2. What is the difference between transverse and longitudinal waves?
3. A wave has a frequency of 50 Hz and a wavelength of 2 m. What is its speed?
4. Give two examples of mechanical waves.
5. Explain the term "interference" in waves.

Challenge Yourself

• Draw a diagram of a transverse wave and label crest, trough, amplitude, and wavelength.
• Describe an experiment to show the reflection of sound waves (echo).

Did You Know?

• Light from the Sun takes about 8 minutes to reach the Earth!
• Bats use sound waves (echolocation) to find their way in the dark.

Glossary

• Amplitude: Maximum displacement from the mean position.
• Wavelength (λ): Distance between two consecutive crests or troughs.
• Frequency (f): Number of waves passing a point per second.
• Transverse Wave: Wave with particle motion perpendicular to wave direction.
• Longitudinal Wave: Wave with particle motion parallel to wave direction.

Answers to Practice Questions

1. Wavelength: The distance between two consecutive crests or troughs.
   Frequency: The number of waves passing a point per second.
2. In transverse waves, particles move perpendicular to the direction of the wave. In longitudinal waves, particles move parallel to the direction of the wave.
3. Speed = frequency × wavelength = 50 × 2 = 100 m/s
4. Sound waves, water waves (any two mechanical waves).
5. Interference is when two waves meet and combine to form a new wave pattern.

---

Understanding waves helps you explore the world of sound, light, and much more in physics!